Experiment 9 – Baking Soda Name __________________
Lab Section __________________
Introduction
The decomposition of any metal hydrogen carbonate will result in the formation of that metal carbonate, water vapor, and carbon dioxide. This lab will investigate the decomposition of sodium hydrogen carbonate, NaHCO
3
, commonly called baking soda. It is governed by the following chemical equation:
2 𝑁𝑎𝐻𝐶𝑂
3
(𝑠)

→ 𝑁𝑎
2
𝐶𝑂
3
(𝑠) + 𝐻
2
𝑂 (𝑔) + 𝐶𝑂
2
(𝑔)
In this lab, the NaHCO
3
will be decomposed to form Na
2
CO
3
. The first half of the experiment will use a pure sample of NaHCO
3
, and the second part will use a mixture containing only some
NaHCO
3
. Depending on how well the first half of the experiment is performed, the percent yield of this reaction should be 100%. The second half of the experiment should see something less than 100%, since it is not a pure sample.
Percent yield is defined as the actual yield divided by the theoretical yield. The actual yield is the amount of product one produces during the experiment. The theoretical yield is the amount of product one should have produced. 𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
% 𝑌𝑖𝑒𝑙𝑑 = 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
𝑥 100%
Unless there are experimental errors, the % Yield should not be over 100%. In many cases, especially ones in which the reaction is difficult to control; the % Yield can be much lower than
100%.
In the case of impure samples, like in the second half of this lab, the % Yield can give the percent of active material in the sample. The concept is the same. The only trick is to keep track of which value is the actual amount, and which is the theoretical amount.
Refer to the sample calculations for more insight.
Equipment
100 or 250 mL beaker
Watchglass
Bunsen burner
Wire gauze
Iron ring
NaHCO
3
Unknown sample

Experiment 9 – Baking Soda Name __________________
Lab Section __________________
Examples
Percent Yield from a Pure Sample
A 0.685 g sample of Ca(HCO
3
)
2
is decomposed by heating to form CaCO
3
. When the sample is cooled it weighs 0.418 g. Calculate the theoretical yield of CaCO
3
.
𝐶𝑎(𝐻𝐶𝑂
3
)
2
(𝑠)

→ 𝐶𝑎𝐶𝑂
3
(𝑠) + 𝐻
2
𝑂 (𝑔) + 𝐶𝑂
2
(𝑔)
To find the theoretical yield, calculate the amount of CaCO
3
one expects to obtain from the
Ca(HCO
3
)
2
. Set up the mass-mole-mole-mass calculation is as follows:
0.685 𝑔 𝐶𝑎(𝐻𝐶𝑂
3
)
2
[
1 𝑚𝑜𝑙 𝐶𝑎(𝐻𝐶𝑂
3
)
2
162.12 𝑔 𝐶𝑎(𝐻𝐶𝑂
3
)
2
] [
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂
3
1 𝑚𝑜𝑙 𝐶𝑎(𝐻𝐶𝑂
3
)
2
] [
100.19 𝑔 𝐶𝑎𝐶𝑂
3 ]
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂
3
= 0.422907 𝑔 𝐶𝑎𝐶𝑂
3 in proper sig figs = 𝟎. 𝟒𝟐𝟑 𝒈 𝑪𝒂𝑪𝑶
𝟑
Theoretical Yield
The percent yield is actual yield divided by the theoretical yield. After decomposition, the actual yield of CaCO
3
was 0.418 g. Divide this actual yield by the theoretical yield and convert to percentage.
% 𝐶𝑎𝐶𝑂
3
= 𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
𝑥 100%
% 𝐶𝑎𝐶𝑂
3
=
0.418𝑔
0.423𝑔
𝑥 100%
% 𝑪𝒂𝑪𝑶
𝟑
= 𝟗𝟖. 𝟖%

Experiment 9 – Baking Soda Name __________________
Lab Section __________________
Percent of Active Material in Unknown Mixture
A 1.425 g sample of powder contains KHCO
3
and an unknown amount of unreactive salt. When it is decomposed it weighed 1.225 g. Calculate the %KHCO
3
in the unknown powder.
2 𝐾𝐻𝐶𝑂
3
(𝑠)

→ 𝐾
2
𝐶𝑂
3
(𝑠) + 𝐻
2
𝐶𝑂
3
(𝑔)
The only mass that is truly known in this problem is the mass that was lost, namely the H
2
O and
CO
2
(grouped as H
2
CO
3
(g) in the equation above).
The mass of gas that was produced is merely the mass before heating minus the mass after heating: 1.425 g – 1.225 g = 0.200 g gas released.
Using this mass, we can determine the actual amount of KHCO
3
that produced this gas by the following mass-mole-mole-mass calculation:
0.200 𝑔 𝐻
2
𝐶𝑂
3
[
1 𝑚𝑜𝑙 𝐻
2
60.03 𝑔 𝐻
2
𝐶𝑂
3
𝐶𝑂
3
] [
2 𝑚𝑜𝑙 𝐾𝐻𝐶𝑂
3
1 𝑚𝑜𝑙 𝐻
2
𝐶𝑂
3
] [
100.02 𝑔 𝐾𝐻𝐶𝑂
3
1 𝑚𝑜𝑙 𝐾𝐻𝐶𝑂
3
]
= 0.666467 𝑔 𝐾𝐻𝐶𝑂
3
In proper sig figs = 𝟎. 𝟔𝟔𝟔 𝒈 𝑲𝑯𝑪𝑶
𝟑
Actual amount of KHCO
3
in sample
The original sample was 1.425 g. If all of the sampler were KHCO
3
, then the amount of gas released would be much more (0.428 g, using the same calculation as in the first example). In this case we see that our calculated value above is the actual amount of KHCO
3
that made the gas, and our initial measured amount in the problem statement is the theoretical amount that should have made the gas.
The percent of active material is the amount of KHCO
3
that decomposed (made the gas) divided by the total amount of material.
% 𝐾𝐻𝐶𝑂
3 𝑎𝑚𝑜𝑢𝑛𝑡 𝑑𝑒𝑐𝑜𝑚𝑝𝑜𝑠𝑒𝑑
= 𝑡𝑜𝑡𝑎𝑙 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙
𝑥 100%
% 𝐾𝐻𝐶𝑂
3
=
0.666𝑔
1.425𝑔
𝑥 100%
% 𝑲𝑯𝑪𝑶
𝟑
= 𝟒𝟔. 𝟕%

Experiment 9 – Baking Soda Name __________________
Lab Section __________________
Procedure
Percent Yield of Na
2
CO
3
from pure NaHCO
3
Weigh out approximately 1 g of NaHCO
3
into your beaker.
Place the watchglass on the beaker. This will act as the indicator of when the experiment is done.
Place the beaker on the wire gauze and heat the NaHCO
3
. A vigorous flame will be used in this experiment. Be sure that the tip of the cone of the flame is touching the wire gauze.
Water droplets should begin to form on the watchglass within a few minutes. Note: the initial “fog” one sees upon heating is merely the water vapor that is naturally occurring on the glass being driven off by the heat.
Continue to heat the NaHCO
3
until the water droplets on the watchglass have disappeared.
Allow the beaker to cool to room temperature and weigh it. This is the mass of the Na
2
CO
3 resulting from the decomposition.
Calculate the theoretical yield of the Na
2
CO
3
from the original mass of the NaHCO
3
.
Percent of NaHCO
3
in an Unknown Mixture
Weigh out approximately 1 to 2 g of the unknown sample into your beaker.
Repeat the steps of the previous procedure. This time, however, the resulting mass is the expected Na
2
CO
3
and the unreactive component of the unknown.
Use the mass lost in the experiment, the H
2
CO
3
gas, to determine the mass of NaHCO
3
in your unknown sample.
Post Experiment Instructions
All waste can be placed in the trash or rinsed down the sink.
Return unknown vial to its place of origin.
Figure 9.1: Setup of Decomposition

Experiment 9 – Baking Soda Name __________________
Lab Section __________________
Prelaboratory Questions
A 0.685 g sample of NaHCO
3
is decomposed by heating to form Na
2
CO
3
. When the sample is cooled it weighs 0.418 g. Calculate the theoretical yield of Na
2
CO
3
. Calculate the percent yield of Na
2
CO
3
.
2 𝑁𝑎𝐻𝐶𝑂
3
(𝑠)

→ 𝑁𝑎
2
𝐶𝑂
3
(𝑠) + 𝐻
2
𝐶𝑂
3
(𝑔)
A 4.076 g sample of powder contains LiHCO
3
and an unknown amount of unreactive salt. When it is decomposed it weighed 1.496 g. Calculate the %LiHCO
3
in the unknown powder.
2 𝐿𝑖𝐻𝐶𝑂
3
(𝑠)

→ 𝐿𝑖
2
𝐶𝑂
3
(𝑠) + 𝐻
2
𝐶𝑂
3
(𝑔)

Experiment 9 – Baking Soda
Data Table
Percent Yield of Na
2
CO
3
from a pure sample of NaHCO
3
Trial 1
Mass of NaHCO
3
(before heating)
Mass of Na
2
CO
3
(after heating)
__________
__________
Name __________________
Lab Section __________________
Trial 2
__________
__________
Theoretical Yield of Na
2
CO
3
– show calculations
Theoretical Yield of Na
2
CO
3
Percent Yield of Na
2
CO
3
– show calculations
__________
Percent Yield of Na
2
CO
3
__________
Average percent yield of Na
2
CO
3
__________
__________
__________

Experiment 9 – Baking Soda Name __________________
Lab Section __________________
Percent of NaHCO
3
in an Unknown Mixture Unknown Number ____
Trial 1 Trial 2
Mass of Unknown Mixture
Before Heating
Mass of Unknown Mixture
After Heating
Mass of gas released, H
2
CO
3
__________
__________
__________
__________
__________
__________
Mass of NaHCO
3
in Unknown Mixture – show calculations
Mass of NaHCO
3
in Unknown Mixture __________
Percent of NaHCO
3
in Unknown Mixture – show calculations
__________
Percent of NaHCO
3
in Unknown Mixture __________
Average Percent of NaHCO
3
in Unknown Mixture __________
__________

Experiment 9 – Baking Soda Name __________________
Lab Section __________________
Postlaboratory Questions
1) A 1.897 g sample of Mg(HCO
3
)
2
was heated and decomposed. When the sample cooled, it weighed 1.071 g. What is the % Yield of this reaction?
2) An geologist brought in a sample of ore containing Fe(HCO
3
)
3
and some other, unreactive material. If the sample weighed 1.394 g before it was decomposed, and 0.978 g after, what is the
%Fe(HCO
3
)
3
of the sample?

Experiment 9 – Baking Soda Name __________________
Lab Section __________________
3) A 1.112 g strip of magnesium is dropped into a giant container of HCl (aq). What is the volume of the gas that is produced at 0°C and 1 atm?
4) Calcium metal is dropped into water, and 15.7 L of gas is produced at STP, what was the mass of calcium that produced the gas?
5) If 2.112 g of Fe
2
O
3
reacts with 0.687 g of Al, how much pure Fe will be produced?

𝐹𝑒
2
𝑂
3
(𝑠) + 2 𝐴𝑙 (𝑠) → 𝐴𝑙
2
𝑂
3
(𝑠) + 2 𝐹𝑒(𝑠)